1. Field of the Invention
This invention relates to digital color image display methods, and more particularly, to a method of displaying an original high-resolution digital color image on a low-resolution dot-matrix display such as an LCD.
2. Description of Related Art
Conventional displays for computers are typically composed of a rectangular array of a specific number of pixels. For instance, a VGA (Video Graphics Adapter) display includes a 640.times.480 array of pixels, an XGA (Extended Graphics Array) display includes a 1024.times.768 array of pixels, and an SVGA (Super Video Graphics Array) display includes a 1280.times.1024 array of pixels. The number of pixels on the display is also referred to as the resolution of the display. For color displays, each pixel is further composed of three dots, respectively used to display the three primary colors, i.e., red (R), green (G), and blue (B), in various intensities, that can be combined to show a specific color. Therefore, the number of dots on a color display is 3 times the resolution. In the case of a VGA display, for example, the total number of dots is 3.times.640.times.480=1920.times.480. By contrast, the LCD is a low-resolution display. An LCD consisting of a 280.times.220 array of dots, for example, can display monochrome images in a resolution of 280.times.220, but will display color images in a reduced resolution of only 93.times.220. This is because that in the latter case, three dots are used in combination to display the respective RGB components of a specific color; therefore 280/3.apprxeq.93.
Conventional methods for displaying an original high-resolution digital color image on a low-resolution LCD require complex computations or direct sampling. To obtain the low-resolution image, the high-resolution image first undergoes an averaging process or is filtered to obtain the RGB values of each pixel in the low-resolution LCD. These RGB data are then used to drive the pixels of the LCD to display the image.
FIG. 1A is a flow diagram showing the procedural steps of a conventional method for displaying an originally high-resolution digital color image on a low-resolution LCD. In this method, the first step is to obtain the original high-resolution digital color image. The second step is to perform a complex computation process so as to transform the image data into a suitable form that can be displayed on the LCD. In the case of displaying an original 640.times.480 VGA color image on a 280.times.220 LCD, each pixel in the LCD represents a group of 7 pixels, where the number 7 is obtained by rounding up the value of 640/93 to the nearest integer number. Therefore, each group of 7 consecutive pixels on each horizontal line of the original high-resolution image is averaged in its RGB values. The third step is then to use the averaged RGB values to drive each corresponding pixel in the LCD.
FIG. 1B is a flow diagram showing the procedural steps of another conventional method for displaying an original high-resolution digital color image on a low-resolution LCD. In this method, the first step is to obtain the original high-resolution digital color image. Then, the second step is to perform a direct sampling process so as to transform the high-resolution image into a suitable form that can be displayed on the LCD. In the case of displaying an original 640.times.480 VGA color image on a 280.times.220 LCD, each pixel in the LCD represents a group of 7 pixels, where the number 7 is obtained by rounding up the value of 640/93 to the nearest integer number. This method differs from the previous method of FIG. 1A in that the RGB values of a particular pixel, for example the 4th one, in each group of 7 consecutive pixels in the original high-resolution image is selected as the RGB values of the corresponding pixel in the LCD. The third step is then to use the averaged RGB values to drive each corresponding pixel in the LCD.
The foregoing two conventional methods, however, are disadvantageous in utilization. For instance, the method of FIG. 1A requires very complex hardware/software means to perform the computations for the transformation, which makes the implementation cost quite high. In the method of FIG. 1B, the direct sampling process has the drawbacks of causing loss of details and abrupt changes in color rendition between neighboring pixels since the RGB values are extracted from one of the 7 pixels in each group. The resulting image displayed on the LCD is thus considerably lower in fidelity when compared to the original one.